Step 2

In the bowl of an electric mixer fitted with the paddle attachment, mix the butter with the dark brown sugar until light and fluffy, 4 to 5 minutes.

Step 3

Add the egg and vanilla extract to the bowl and mix until combined, 1 minute more. Add the flour and salt, and mix until fully incorporated.

Step 4

Cut a piece of parchment paper the size of a baking sheet. Place the dough on the long side of the paper. The dough will be sticky, so use the paper to help you roll it into a rounded log shape, about 17 to 19 inches long (which is about the length of a baking sheet) and 1½ inches wide.

Step 5

Once you've formed a log, make sure the dough is completely wrapped in the parchment paper. Refrigerate for at least 2 hours or up to overnight. (Note: The dough can be frozen at this point for up to three months.)

Step 6

Preheat the oven to 350°F. Line two baking sheets with parchment paper.

Step 7

Slice the log of cookie dough into ¼-inch thick slices and transfer to the baking sheets. Leave at least ¾ inch around each cookie to allow room for spreading.

Step 8

Bake the cookies until they are slightly golden around the edges, 8 to 10 minutes. Cool completely before decorating.

Step 9

Place the butterscotch chips in a microwave-safe bowl and melt the chips in the microwave in 10-second blasts, stirring as needed. Use a spoon to drizzle the melted butterscotch over the cookies. Let rest until set. Store leftover cookies in an airtight container at room temperature for up to a week.